Effects of Fatigue on Voluntary Electromechanical and Relaxation Electromechanical Delay

2017 ◽  
Vol 38 (10) ◽  
pp. 763-769 ◽  
Author(s):  
Cory Smith ◽  
Terry Housh ◽  
Ethan Hill ◽  
Joshua Keller ◽  
Glen Johnson ◽  
...  
Keyword(s):  
Vastus Lateralis ◽  
Force Production ◽  
Elastic Component ◽  
Electromechanical Delay ◽  
Excitation Contraction Coupling ◽  
Contraction Coupling ◽  
Series Elastic Component ◽  
Before And After ◽  
Electromyographic Signal ◽  
Series Elastic

AbstractThe purposes of the present study were to examine: 1) the effects of fatigue on electromechanical delay from the onsets of the electromyographic signal to force production (EMDE-F), the onsets of the electromyographic to mechanomyographic signals (EMDE-M), the onsets of the mechanomyographic signal to force production (EMDM-F), as well as the cessations of the electromyographic to force production (R-EMDE-F), cessation of the electromyographic to mechanomyographic signals (R-EMDE-M), and cessations of the mechanomyographic signal to force production (R-EMDM-F); and 2) the relative contributions from EMDE-M and EMDM-F to EMDE-F as well as R-EMDE-M and R-EMDM-F to R-EMDE-F from the vastus lateralis in non-fatigued and fatigued states. The values EMDE-F, EMDE-M, EMDM-F, R-EMDE-F, R-EMDE-M and R-EMDM-F were calculated during maximal voluntary isometric contractions, before and after 70% 1-repetition maximum leg extensions to failure. There were significant pretest to posttest increases in EMDE-F (73%;p<0.01), EMDE-M (99%;p<0.01), EMDM-F (60%;p<0.01), R-EMDE-F (101%;p<0.01) and R-EMDM-F (368%;p<0.01), but no significant change in R-EMDE-M (25%;p=0.46). Fatigue-induced increase in EMDE-F indicated excitation-contraction coupling failure (EMDE-M) and increases in the compliance of the series elastic component (EMDM-F). Increases in R-EMDE-F were due to increases in relaxation time for the series elastic component (R-EMDM-F), but not changes in the reversal of excitation-contraction coupling (R-EMDE-M).

Electromechanical delay revisited using very high frame rate ultrasound

2009 ◽  
Vol 106 (6) ◽  
pp. 1970-1975 ◽  
Author(s):  
Antoine Nordez ◽  
Thomas Gallot ◽  
Stefan Catheline ◽  
Arnaud Guével ◽  
Christophe Cornu ◽  
...  
Keyword(s):  
Frame Rate ◽  
Active Part ◽  
Elastic Component ◽  
Myotendinous Junction ◽  
Electromechanical Delay ◽  
Gastrocnemius Medialis ◽  
High Frame Rate ◽  
Series Elastic Component ◽  
Very High ◽  
Series Elastic

Electromechanical delay (EMD) represents the time lag between muscle activation and muscle force production and is used to assess muscle function in healthy and pathological subjects. There is no experimental methodology to quantify the actual contribution of each series elastic component structures that together contribute to the EMD. We designed the present study to determine, using very high frame rate ultrasound (4 kHz), the onset of muscle fascicles and tendon motion induced by electrical stimulation. Nine subjects underwent two bouts composed of five electrically evoked contractions with the echographic probe maintained over 1) the gastrocnemius medialis muscle belly (muscle trials) and 2) the myotendinous junction of the gastrocnemius medialis muscle (tendon trials). EMD was 11.63 ± 1.51 and 11.67 ± 1.27 ms for muscle trials and tendon trials, respectively. Significant difference ( P < 0.001) was found between the onset of muscle fascicles motion (6.05 ± 0.64 ms) and the onset of myotendinous junction motion (8.42 ± 1.63 ms). The noninvasive methodology used in the present study enabled us to determine the relative contribution of the passive part of the series elastic component (47.5 ± 6.0% of EMD) and each of the two main structures of this component (aponeurosis and tendon, representing 20.3 ± 10.7% and 27.6 ± 11.4% of EMD, respectively). The relative contributions of the synaptic transmission, the excitation-contraction coupling, and the active part of the series elastic component could not be directly quantified with our results. However, they suggest a minor role of the active part of the series elastic component that needs to be confirmed by further experiments.

The abrupt transition from rest to activity in muscle

1949 ◽  
Vol 136 (884) ◽  
pp. 399-420 ◽  
Keyword(s):  
Isometric Force ◽  
Sudden Change ◽  
Active State ◽  
Elastic Component ◽  
Series Elastic Component ◽  
Full Activity ◽  
Change Of State ◽  
Set Up ◽  
Full Intensity ◽  
Series Elastic

The internal mechanical condition of an excited muscle has been examined by applying quick stretches at various moments after a maximal shock. At the end of the latent period there is an abrupt change of state, the contractile component suddenly becoming capable of bearing a load equal to the maximum tension set up in an isometric tetanus. The intensity of the active state produced by a shock is greatest at the start, is maintained for a time and then declines as relaxation sets in. The properties of the fully active state are defined by the three constants of the characteristic equation relating speed of shortening to load. A muscle consists mechanically of three components: (1) a contractile one, (2) an undamped series elastic one and (3) a parallel elastic one. The complication provided by (3) is avoided by working with small initial loads. The load-extension relation of the series elastic component has been determined. Its extensibility is high at small loads, becoming much less at greater ones. The full isometric force produces an extension in it of about 10% of the muscle’s length. In an isometric tetanus the form of the myogram is fully determined by the characteristic force-velocity relation of the contractile component and the load-extension curve of the series elastic one, the former having to shorten and stretch the latter before an external tension can be manifested. In a twitch there is insufficient time, before relaxation sets in, for the full tension to be developed. When the tension is raised sufficiently by a quick stretch applied early after a shock the contractile component cannot shorten as it would normally and the heat of shortening is absent. The heat of activation is probably a by-product of the process by which the sudden change of state from rest to full activity occurs. When a muscle is subjected to a tension rather greater than it can bear it lengthens slowly; to a tension considerably greater it ‘gives’ or ‘slips’. When a muscle is stretched rapidly a transitory overshoot of tension occurs followed by ‘slip’. During the disappearance of this extra tension heat is produced, as in the ‘cold drawing’ of a wire or thread. An analogous process occurs in relaxation under a load. When two shocks are applied in succession, the second restores the active state to its full intensity, from which it has declined to an extent depending on the interval after the first one. If, under isometric conditions, the series elastic component is still partly stretched at the moment when the second response occurs, the total tension developed is greater. This is the origin of the so-called ‘supernormal phase’ and the basis of the greater tension maintained in atetanic contraction. During a tetanus each shock restores the active state of the muscle to its full intensity. It seems reasonably certain that excitation of a muscle fibre occurs at its surface. It has been suggested that contraction is set up inside by the arrival of some chemical substance diffusing inwards after liberation a t the surface. The onset, however, of full activity occurs so soon after a shock that diffusion is far too slow to account for it. A process, not a substance, must carry activation inwards.

Effects of eccentric training on mechanical properties of the plantar flexor muscle-tendon complex

2013 ◽  
Vol 114 (5) ◽  
pp. 523-537 ◽  
Author(s):  
Alexandre Fouré ◽  
Antoine Nordez ◽  
Christophe Cornu
Keyword(s):  
Mechanical Properties ◽  
Achilles Tendon ◽  
Plantar Flexion ◽  
Triceps Surae ◽  
Elastic Component ◽  
Plantar Flexor ◽  
Eccentric Training ◽  
Tendon Stiffness ◽  
Series Elastic Component ◽  
Series Elastic

Eccentric training is a mechanical loading classically used in clinical environment to rehabilitate patients with tendinopathies. In this context, eccentric training is supposed to alter tendon mechanical properties but interaction with the other components of the muscle-tendon complex remains unclear. The aim of this study was to determine the specific effects of 14 wk of eccentric training on muscle and tendon mechanical properties assessed in active and passive conditions in vivo. Twenty-four subjects were randomly divided into a trained group ( n = 11) and a control group ( n = 13). Stiffness of the active and passive parts of the series elastic component of plantar flexors were determined using a fast stretch during submaximal isometric contraction, Achilles tendon stiffness and dissipative properties were assessed during isometric plantar flexion, and passive stiffness of gastrocnemii muscles and Achilles tendon were determined using ultrasonography while ankle joint was passively moved. A significant decrease in the active part of the series elastic component stiffness was found ( P < 0.05). In contrast, a significant increase in Achilles tendon stiffness determined under passive conditions was observed ( P < 0.05). No significant change in triceps surae muscles and Achilles tendon geometrical parameters was shown ( P > 0.05). Specific changes in muscle and tendon involved in plantar flexion are mainly due to changes in intrinsic mechanical properties of muscle and tendon tissues. Specific assessment of both Achilles tendon and plantar flexor muscles allowed a better understanding of the functional behavior of the muscle-tendon complex and its adaptation to eccentric training.

Optimal stiffness of series elastic component in a stretch-shorten cycle activity

1991 ◽  
Vol 70 (2) ◽  
pp. 825-833 ◽  
Author(s):  
G. J. Wilson ◽  
G. A. Wood ◽  
B. C. Elliott
Keyword(s):  
Natural Frequency ◽  
Bench Press ◽  
Elastic Component ◽  
Series Elastic Component ◽  
Damped Oscillations ◽  
Movement Frequency ◽  
Experienced Male ◽  
Weight Lifters ◽  
Optimal Stiffness ◽  
Series Elastic

Twelve experienced male weight lifters performed a rebound bench press and a purely concentric bench press lift. Data were obtained pertaining to 1) the benefits to concentric motion derived from a prior stretch and 2) the movement frequency adopted during performance of the stretch-shorten cycle (SSC) portion of the rebound bench press lift. The subjects also performed a series of quasi-static muscular actions in a position specific to the bench press movement. A brief perturbation was applied to the bar while these isometric efforts were maintained, and the resulting damped oscillations provided data pertaining to each subject's series elastic component (SEC) stiffness and natural frequency of oscillation. A significant correlation (r = -0.718, P less than 0.01) between maximal SEC stiffness and augmentation to concentric motion derived from prior stretch was observed. Subjects were also observed to perform the SSC portion of the rebound bench press movement to coincide with the natural frequency of oscillation of their SEC. These results are interpreted as demonstrating that the optimal stiffness in a rebound bench press lift was a resonant-compliant SEC.

Caffeine’s Beneficial Effect on Maximal Voluntary Strength and Activation in Uninjured but Not Injured Muscle

2008 ◽  
Vol 18 (6) ◽  
pp. 639-652 ◽  
Author(s):  
Nicole D. Park ◽  
Robert D. Maresca ◽  
Kimberly I. McKibans ◽  
D. Reid Morgan ◽  
Timothy S. Allen ◽  
...  
Keyword(s):  
Repeated Measures ◽  
Muscle Activation ◽  
Eccentric Contraction ◽  
Knee Extensors ◽  
Double Blind ◽  
Maximal Voluntary Isometric Contraction ◽  
Caffeine Ingestion ◽  
Excitation Contraction Coupling ◽  
Contraction Coupling ◽  
Before And After

The study’s objective was to determine whether orally ingested caffeine could help overcome excitation-contraction-coupling failure, which has been suggested to explain part of the strength loss associated with eccentric-contraction-induced muscle injury. A sample of 13 college students (4 men and 9 women) was used in a double-blind, repeated-measures experimental design. Each participant performed 2 experimental trials, 1 with each leg, with each trial lasting 4 consecutive days. On a given day, each participant was randomly assigned to ingest a capsule containing 6 mg/kg of either caffeine or flour (placebo). On the day of and the first 2 days after a bout of 50 injurious eccentric contractions done by the knee extensors, the interpolated-twitch technique was used to assess electrically evoked strength, maximal voluntary isometric contraction (MVIC) strength, and percent muscle activation during MVIC both before and after capsule ingestion. These variables were also measured before and after capsule ingestion the day before the eccentric-contraction bout—when the muscle was uninjured. In injured muscle, caffeine had no effect on any variable. In uninjured muscle, caffeine also had no effect on electrically evoked strength but increased MVIC strength by 10.4% compared with placebo (p = .00002), and this was attributed to an increase in muscle activation (6.2%; p = .01). In conclusion, the data provide no evidence that caffeine ingestion can help overcome excitation-contraction-coupling failure, if it exists, in injured human muscle. The data do indicate that caffeine ingestion can increase MVIC strength and activation in uninjured muscle but not in injured muscle.

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